Nope - they assume you did the exam sitting at home relaxing next to the fire while your mum brings you cake and hot chocolate

Lol, of course they know candidates get nervous and are given a time limit! This is probably most evident at the end of long written exams (History, English etc) where candidates will tend to write down all their remaining ideas. However, rest assured that examiners have years upon years of experience and are definitely aware of nerves and timing. They will mark all scripts equally and make sure that grade boundaries are set fairly (taking into account candidates' performance)